A power supply apparatus is provided which includes a power supply; a DC/DC converter including a switching element of an upper arm, a switching element of a lower arm and a reactor; a first switch provided between the switching element of the lower arm and the negative electrode of the power supply, the first switch being normally closed; a power supply fuse provided between the positive electrode of the power supply and the other end of the reactor; a second power supply fuse connected to the power supply fuse in parallel; a second switch connected to the second power supply fuse in series and connected to the power supply in parallel, the second switch being normally opened; and a controller that opens the first switch and closes the second switch upon a short circuit failure of the switching element of the lower arm being detected.
